1. Field of the Invention
The present invention relates to a binder for foundry sand. More particularly, the present invention relates to a binder for molds by which a foundry process is carried out at a relatively low temperature to form founded products of aluminum alloy, etc., inter alia, a binder for forming a core. Further, it relates to a binder for foundry sand comprising methylolmelamine or alkylated methylolmelamine and a water soluble organic compound having a hydroxyl group.
2. Description of Prior Art
The shell mold method, in which sand coated with a binder of a phenol resin is formed with heat to make a foundry mold is well known. However, if a core obtained by that method is applied in a low-temperature process, especially of an aluminum alloy, it is very difficult to take off the sand after molding because the disintegratability of the core is insufficient. Besides, such conventional sand coated with the binder of phenol resin generates a strong bad smell during core formation or when pouring the melting metal. An improvement in this working environment has been desired.
After intensive studies, the inventors have found that a binder composed of methylolmelamine or alkylated methylolmelamine and a water soluble organic compound having a hydroxy group, for example, monosaccharide, oligosaccharide, polysaccharide, water soluble cellulose derivatives, polyhydric alcohols and so on, has excellent properties as a binder for coated sand used in the low-temperature foundry.
It is known that methylolmelamine or an alkyl ether thereof, that is, alkylated methylolmelamine which is a reaction product of melamine and formaldehyde, can be used as a binder for foundry sand.
Sand coated with methylolmelamine or alkylated methylolmelamine is better than sand coated with a phenol resin in respect to the disintegrating property, but when cast and molded, generates a large volume of gases having a bad smell and has a great hygroscopicity. For these reasons, it has not been much used to date. It has no special advantage compared with the sand coated with phenol resin when iron is cast at a high temperature.